In 1968 Anthony Doob and Alan Gross, of the University of Toronto and the University of Wisconsin, published a response-to-horn- honking study that triggered an expanded study, seven years later, by a team at the University of Utah.

Doob and Gross: Honking"Status of Frustrator as an Inhibitor of Horn-Honking Responses," Anthony N. Doob and Alan Gross, Journal of Social Psychology, vol. 76, 1968, pp. 213--8. The authors explain:

One of two automobiles, a new luxury model or an older car, was driven up to a signal controlled intersection and stopped. The driver was instructed to remain stopped after the signal had changed to green until 15 seconds had elapsed, or until the driver of the car immediately behind honked his horn twice. Subjects were the 82 drivers, 26 women and 56 men, whose progress was blocked by the experimental car. The experiment was run from 10:30 A.M. to 5:30 P.M. on a Sunday, in order to avoid heavy weekday traffic....

Forty-seven percent of the subjects in the low status condition honked twice at the experimental car, as compared to 19 percent of the subjects in the high status condition. This difference should be interpreted cautiously because it is confounded with the main result that more people honk generally in the low status condition. Of those who overcame the inhibition to honk at all, 56 percent in the low status condition and 39 percent in the high status condition honked a second time, a difference which was not significant.

Detail from the study "Status of Frustrator as an Inhibitor of Horn-Honking Responses."

Three studies extended laboratory research on aggression to a naturalistic setting which involved horn honking from drivers as a measure of aggression; the studies were adapted from Doob and Gross. The results from a survey (Study 1) of 59 drivers suggested that they were frequently irritated by and aggressive toward other drivers. A second study (using a 3x2 factorial design with 92 male drivers) indicated that manipulations of a rifle in an aggressive context and victim visibility (dehumanization) both significantly influenced horn honking rates subsequent to obstruction at a signal light. A third study with 137 male drivers and 63 female drivers examined the interactive effects of a rifle, an aggressively connotated bumper sticker, and individual subject characteristics (sex and an exploratory index of self-perceived status) on horn honking.